The following relates to optical detectors, radiometers, imagers, and so forth. It finds particular application in conjunction with silicon-based millimeter-wavelength detectors, radiometers, and imagers, and will be described with particular reference thereto. However, the following is amenable to other like applications such as detectors, radiometers, and imagers operating in other wavelength ranges.
Passive imaging systems and radiometers employ detectors operating at millimeter-wave frequencies. Biased Schottky diodes are commonly used for these applications. However, the biasing circuit greatly increases the system and pixel complexity and also leads to extra noise and drift.
Zero-bias diode detectors are advantageous because no biasing circuit is required. Zero-bias diode detectors should have a large zero bias nonlinearity or curvature. Discrete Ge backward diodes and planar-doped barrier GaAs diodes have previously been used for zero bias detection with high nonlinearity. However, because of the chosen substrates (germanium substrates for Ge backward diodes and GaAs substrates for planar-doped barrier GaAs diodes), these devices are not readily amenable to imaging applications, where a mass-producible technology is required to fabricate a large number of identical devices into compact pixelated imaging arrays. Recently, Sb-based heterojunction backward diodes were realized that are candidates for zero-bias detector applications due to their high sensitivity, high bandwidth, modest temperature dependence and mass production capability. However, the high cost of Sb-based backward diodes and their incompatibly with main-stream silicon read-out circuitry are problematic.